Today i received a question about how to serialize an arraylist through xmlserialization.
Then i rapidly wrote a class named MyData which has 2 properties

public class MyData
 {
     public int a;
     public string b;
     public MyData()
     { }
     public MyData(int _a, string _b)
     {
         a = _a;
         b = _b;
     }
 }

Then generated some instances and added them to an arraylist in the main project.

class Program
 {
     static void Main(string[] args)
     {
         RunIt();
     }
     static void RunIt()
     {
         MyData v1 = new MyData(0, "Zero");
         MyData v2 = new MyData(1, "One");
         MyData v3 = new MyData(2, "Two");

         ArrayList al = new ArrayList();
         al.Add(v1);
         al.Add(v2);
         al.Add(v3);

         XmlSerializer s = new XmlSerializer(typeof(ArrayList));
         string path = @"c:\seri.xml";
         TextWriter tx = new StreamWriter(path, true);
         s.Serialize(tx, al);
         tx.Close();

         FileStream fs = File.OpenRead(@"c:\seri.xml");
         ArrayList ax = (ArrayList)s.Deserialize(fs);

         Console.WriteLine(((MyData)ax[0]).a.ToString());
         Console.WriteLine(((MyData)ax[1]).a.ToString());
         Console.WriteLine(((MyData)ax[2]).a.ToString());

     }
 }

When i ran the code i got the error, {"The type ConsoleApplication1.MyData was not expected. Use the XmlInclude or SoapInclude attribute to specify types that are not known statically."} which was the main question.

After some search i found out tht XmlSerializer was not aware of the type of MyData class and thus i got the above error.
To make XmlSerializer aware of a custom type, you should use one of it's constructer methods while u'r creating the object.
While creating XmlSerializer object i just added type type of my arraylist includes.

XmlSerializer s = new XmlSerializer(typeof(ArrayList),new Type[]{typeof(MyData)});

Ps: also i found out tht if u're developing this kind of code and having these type of errors, everytime u run the project make sure u delete the serialization file.Cause previous failed attemps may cause the right code to throw exceptions.